1. Field of the Invention
The invention relates to a keyboard, more particularly to a keyboard control circuit.
2. Description of the Related Art
A conventional keyboard control circuit for a keyboard having 144 (18×8) keys includes an array module and a processing unit. The array module includes 18 scan lines, 8 return lines that intersect the scan lines to form 144 intersections, and 144 key switches each disposed at a corresponding intersection and operable to control conduction between a corresponding scan line and a corresponding return line intersecting each other at the corresponding intersection. The processing unit provides a scan signal to each of the scan lines during a scan period, receives at least one scan signal from the return lines in response to operation of at least one of the key switches, and outputs an input signal corresponding to operation of the at least one of the key switches.
Assume that four key switches (A, B, C, D) are disposed respectively at first, second, third and fourth intersections that are formed by first and second scan lines (x1, x2) and first and second return lines (y1, y2) such that the first, second, third and fourth intersections respectively have a scan line coordinate and a return line coordinate indicated by (x1, y1), (x2, y1), (x1, y2), and (x2, y2) When the key switches (A, B, C) are simultaneously operated, the processing unit receives the scan signal from the first return line (y1) through the first and second scan lines (x1, x2) and from the second return line (y2) through the first scan line (x1). However, the processing unit further receives the scan signal from the second return line (y2) through the second scan line (x2), even though the key switch (D) is not operated. As such, the fourth intersection is regarded as a ghost key position.
In gaming applications, occurrence of ghost keys is not permitted. In order to overcome occurrence of ghost keys, a diode is disposed at each of the intersections. However, due to the presence of the diodes, the array module has a relatively large size, a complicated wiring, and a relatively high cost.